The U.S. FAA adopted a new airworthiness directive (AD) for certain Learjet Model 55, 55B, and 55C airplanes. The AD requires inspecting the installation of the forward light assembly in the aft lavatory to determine the location of the terminal connector; inspecting for damage of the light assembly terminals, wires, and oxygen lines; inspecting to determine if the cable nipple is installed over the light assembly terminal; and doing corrective actions if necessary. This AD also requires installing a clamp to the forward side of the frame to maintain a positive distance between the light assembly and oxygen line. This AD results from a report of a cabin fire in the left-hand upper cabin fuselage above the aft cabin window at frame 23. The AD is issued to detect and correct improper installation of the lavatory light assembly, which could result in contact between the electrical terminals of the light assembly and an adjacent oxygen supply line, and consequent short circuit or fire hazard. (FAA)